The microminiaturization of electronic components has created widespread growth in the use of portable electronic devices such as cellular phones, pagers, video cameras, facsimile machines, portable stereophonic equipment, personal organizers and personal computers. As a result, the demand of improved power sources for these devices has been increased. Moreover, telecommunication backup batteries, hybrid electric vehicles, and electric vehicles also require advanced battery materials to meet the high demand and performance. Preferably, the battery materials are environmentally benign and relatively low cost to make these expanded battery applications practical. Relevant batteries include primary batteries, i.e., batteries designed for use through a single charging cycle, and secondary batteries, i.e., batteries designed to be rechargeable. Some batteries designed essentially as primary batteries may be rechargeable to some extent.
Batteries based on lithium have been the subject of considerable development effort and are being sold commercially. Lithium-based batteries have become commercially successful due to their relatively high energy density. Lithium-based batteries generally use electrolytes containing lithium ions. The negative electrodes for these batteries can include lithium metal or alloy (lithium batteries), or compositions that intercalate lithium (lithium ion batteries). Preferred electroactive materials for incorporation into the positive electrodes are compositions that intercalate lithium. For example, metal phosphates are candidates for the production of cathode materials that intercalate lithium.
An example of lithium-ion battery is the lithium ferrophosphate (LiFePO4, LFP) battery, in which LiFePO4 is used as the cathode material. LFP exhibits some advantages such as low cost, non-toxicity, natural abundance, excellent thermal stability, safety characteristics, electrochemical performance, and specific capacity (170 mA·h/g, or 610 C/g). As such, LFP battery is even finding a number of roles in vehicle use and backup power, among others. However, LFP batteries are still expensive to produce. For instance, in order to manufacture LFP active material and its dopant, one major production method is using iron oxalate as Fe source precursor and NH4H2PO4 as PO4 source precursor. The drawback is that the manufacturing process for iron oxalate and NH4H2PO4 generates hazardous gas, and the processing cost is very high. Another method is the use of fine quality iron phosphate as precursor for both Fe and PO4 source. However, the manufacturing cost for iron phosphate is also very high.
The manufacture of FePO4 also wastes a huge amount of water, and is therefore not environmentally friendly. More than one billion people in the world is water stressed, and do not have access to potable water. About 700 million people in 43 countries face water scarcity, since their annual water supplies drop below 1,000 cubic meters per person per year. In China, more than 538 million people are living in a water-stressed region.
Thus, there is a need of a new method or process of producing LFP and FePO4 at a lower cost and using less water. Advantageously, the present invention provides a novel method of synthesizing a phosphate salt that can overcome the problem.